How long does a propane tank last?
It depends on the tank and what you are burning. A 20 lb grill cylinder runs a grill about 10 hours; a 500 gallon tank runs a whole-house generator for days. The chart and calculator below cover grills, heaters, fire pits, and generators, with the simple math behind them.
Propane duration calculator
runtime per tankThese are estimates. Appliance ratings shown are typical; your own appliance's BTU/hr is on its label and is the number to trust. Gallon-rated tanks are figured at the safe 80% fill. Cold weather slows how fast a small tank can vaporize propane, which can limit output below what the math shows. Never guess at a propane connection: if you smell gas, shut off the tank, ventilate, and call your supplier.
Nonstop runtime by tank and appliance
Runtime running flat out, at the safe 80% fill for gallon tanks. Appliance ratings are typical; your own appliance's rating is on its label.
| Appliance | BTU/hr | 20 lb grill cylinder | 100 lb cylinder | 500 gal ASME tank |
|---|---|---|---|---|
| Gas grill (medium-high) | 40,000 | 10.8 hr | 2.2 days | 38.1 days |
| Patio heater | 40,000 | 10.8 hr | 2.2 days | 38.1 days |
| Fire pit or fire table | 50,000 | 8.6 hr | 43.1 hr | 30.5 days |
| Portable propane heater | 30,000 | 14.4 hr | 3.0 days | 50.8 days |
| Propane generator (about 7 kW) | 112,000 | 3.8 hr | 19.2 hr | 13.6 days |
How the runtime is worked out
Propane holds a fixed amount of energy: about 91,500 BTU per gallon, or 21,548 BTU per pound. A tank's usable energy is its amount times that number, and gallon-rated tanks are filled to 80% for safe expansion room, so a 500 gallon tank gives you 400 usable gallons.
Runtime is then usable BTU divided by the appliance's BTU-per-hour rating. A 20 lb cylinder holds about 430,000 BTU; a 40,000 BTU-per-hour grill divides that into roughly 10.7 hours. Two caveats: cold weather slows how fast a small tank can vaporize propane, which can cap output; and lb-rated cylinders already state the propane weight they hold, so no extra 80% step applies to them.
Common questions
How long does a 20 lb propane tank last on a grill?
A 20 lb grill cylinder holds about 430,000 BTU. A grill on medium-high burns roughly 40,000 BTU an hour, so a full tank runs about 10 to 11 hours of active grilling. Cook a couple of hours at a time and one tank lasts a month or more of weekend cookouts. Turn the burners down and it stretches further.
How long will a propane tank run a generator?
It depends on the load and the tank. A propane generator carrying about a 7 kW load burns roughly 112,000 BTU an hour, so a 20 lb tank lasts under 4 hours, while a 500 gallon tank at the safe 80% fill runs it for well over a week. Lighter loads stretch it a lot. Use the calculator above with your tank and load.
How long does propane last on a patio heater?
A standard patio heater burns around 40,000 BTU an hour on high, the same order as a grill, so a 20 lb tank gives about 10 hours. Turn it down from full and you get considerably more. A larger 100 lb cylinder runs one for roughly two full days of continuous use.
How is propane runtime calculated?
It is simple division. One gallon of propane holds about 91,500 BTU and one pound about 21,548 BTU. Multiply your tank's usable amount (gallon tanks fill to 80% for safety) to get total BTU, then divide by the appliance's BTU-per-hour rating to get hours. The calculator does this for you, at the safe 80% fill.